When actuated, irreversible displays undergo permanent changes in appearance. Initially obscured or otherwise hidden information is revealed by the changes of appearance.
Changes that take place in irreversible displays generally involve the revelation of indicia, which can range from a patch of color to text and pictures. The indicia can be revealed by chemical or physical agents that change themselves or that produce other changes in the displays. For example, opaque coloring agents can be rendered transparent to reveal underlying indicia, or similar agents can change from one color to another to indicate a change.
Chemical transformations in irreversible displays are sometimes used for security purposes to provide evidence of tampering or counterfeiting. U.S. Pat. No. 4,488,646 to McCorkle hides a warning message behind a solvent-sensitive blush coating to provide evidence of solvent tampering with letters, tickets, and other information-bearing constructions. Upon exposure to a wide range of aromatic or aliphatic solvents, the blush coating is transformed into a transparent state revealing the message. U.S. Pat. No. 4,903,991 to Wright discloses a document security system in which a latent image is developed by rupturing photoactive microcapsules to verify authenticity.
Mechanical transformations are more often used for interactive game pieces. The most common are scratch-off games in which an opaque coating is removed by abrasion to reveal a hidden indicium. Chang et al. in U.S. Pat. No. 5,431,452 separately position a latent image and a removable image-developing device on different portions of a substrate. The image-developing device contains a chromogenic composition that converts the latent image into a visible image.
Our irreversible displays exploit features of thin metal films, especially vapor deposited films, for such purposes as temporarily obscuring predetermined indicia from view and subsequently reacting with chemical clearing agents to reveal the predetermined indicia. The thin metal films can be cleared away to reveal underlying indicia, or the indicia can also be formed by clearing the films in predetermined patterns. The clearing process is visually engaging as a preferably lustrous metal progressively disappears.
One example of our irreversible display includes a metal layer having a surface that overlies an indicium, such as a contrasting color, a pattern, or a message. A substrate supports the metal layer and the indicium. A chemical clearing agent is supported on the substrate out of contact with the surface of the metal layer that overlies the indicium. The clearing agent is relatively movable into contact with the surface of the metal layer for inducing a chemical reaction that clears the metal layer and reveals the underlying indicium. The metal layer, which can be formed from a variety of metals including aluminum, zinc, or silver, is preferably thick enough to completely obscure the indicium but thin enough to rapidly disappear when placed in contact with the clearing agent. Thicknesses between 100 and 1000 Angstroms are preferred for these purposes.
The clearing agent can be drawn from a variety of materials including electrolytes, acids, bases, and other agents that participate in localized reactions for corroding or otherwise clearing the metal layer. Among the choices are many safe and environmentally friendly materials including edibles such as juices, carbonated beverages, and even condiments. The reactions that clear the metal layer include localized electrochemical reactions that oxidize the metal layer. In contrast to galvanic or electrolytic electrochemical reactions, the localized electrochemical reactions between the clearing agent and the metal layer produce a mixed electropotential and do not require a net flow of current through the metal layer.
Preferably, the substrate is one of a pair of top and bottom substrates between which the clearing agent is confined within a reservoir out of contact with the surface of the metal layer. The top substrate preferably includes a transparent portion (i.e., a window) that overlies the metal layer and the indicium. A gated pathway between the substrates can be used to direct the clearing agent from the reservoir into contact with the surface of the metal layer.
The reservoir can be arranged adjacent to or even surrounding the surface of the metal layer that overlies the indicium. Squeezing the reservoir forces some of the clearing agent along one or more of the gated pathways into contact with the surface of the metal layer from one or more directions. Alternatively, the clearing agent can be arranged to overlie the metal film at an initial separation set by a spacer. An opening through the spacer allows the clearing agent to be relatively moved into contact with the metal layer. The clearing agent of this overlapping arrangement can be an adhesive for maintaining contact with the surface of the metal layer after being relatively moved through the spacer opening.
Another example of our irreversible display includes a metal film, a display window aligned with the metal film, and an indicium that is aligned with the display window but obscured by the metal film. The window provides access to the metal film for exposing the metal film to a chemical clearing agent that clears a portion of the metal film and reveals the indicium. A separate access opening can also be provided along with a transport medium (e.g., a wick) to transport the clearing agent from the opening to the metal film.
The exemplary display can be activated by adding the clearing agent through the display window or other access opening. Contact between the clearing agent and the metal film produces a localized electrochemical reaction between the clearing agent and the metal film without generating an electromotive force beyond the clearing agent. The localized electrochemical reaction clears the metal film (in an apparent gnawing action) and reveals the indicium within the display window through an opening cleared in the metal film by the reaction with the clearing agent.
Other exemplary approaches for controlling contact between a clearing agent and a metal film include forming a breakable barrier layer and microencapsulating the clearing agent. Mechanical action such as squeezing or bending can be used to breach the barrier layer or release the clearing agent from microencapsulation. Adhesive clearing agents can be separately mounted and temporarily protected by a release liner. Upon removal of the release liner, the adhesive clearing agent can be moved in contact with the metal layer through an opening in the top substrate.
Instead of clearing the metal film to reveal an underlying indicium, the metal film can be cleared in a pattern (e.g., a stencil) that forms its own indicium. For example, a protective layer could be laid out in a pattern on the metal film. Exposing a portion of the metal film that is not covered by the protective layer to a clearing agent changes the exposed metal film from opaque to clear. The remaining portion of the metal film that is covered by the protective layer is sheltered from similar exposure to the clearing agent. The two portions of the metal film are arranged for producing a predetermined pattern upon exposure of the first portion of the metal film to the clearing agent.
Our irreversible displays can be manufactured by an in-line press. All of the layers including substrates, metal films, clearing agents, graphics, adhesives, and spacers can be formed from individual webs or from layers applied to the individual webs. The result is a succession of thin flexible displays that can be manufactured quickly at low cost and integrated if desired with other press-produced or otherwise compatible articles.